The broad objectives of the proposed research are to chart the acquisition and utilization of hierarchical structure among common categories corresponding to terms in the natural language. These objectives will be pursued in three ways: (1) By continuation of a longitudinal study of a small group of children in which comprehension of superordinate terms is examined: (a) by responses to requests for exemplars in the home, (b) with a forced-choice picture selection technique and (c) with probes and requests for justification of classifications. (2) By continuation of a series of studies with children of different ages with the forced-choice picture selection technique. Both extension and preferred exemplars are being examined for superordinate category terms as a function of familiarity and centrality. In addition, choice behavior when obvious (for the adult) exemplars are not presented is being examined for basic level and superordinate category terms and for property terms. (3) The role of hierarchical structure in the support of induction in children and adults will be examined both by the use of structured probes ("Tell me anything you can about..." "What's true of all..." "What kinds of things are....") and requests for consideration of violations of generalizations.